Brake temperature prediction and cooling time functionality

ABSTRACT

A brake cooling period prediction system for predicting a brake cooling period following a braking event, and including a sensor apparatus in communication with a prediction apparatus. The sensor apparatus has a torque sensor for measuring the torque reacted by a brake during a braking event; a wear sensor for measuring a wear state of the brake; and an environmental sensor for measuring at least one ambient condition of the environment of the brake. The prediction apparatus includes a memory storing information relating to the thermal behavior of the brake; and a controller configured to receive a torque measurement, a wear measurement and an ambient condition measurement from the sensor apparatus; and predict a cooling period based on the received torque, wear and ambient condition measurements, and the information relating to the thermal behavior of the brake.

RELATED APPLICATION

This application claims priority to Great Britain patent application no.1607256.3 filed Apr. 26, 2016, the entire content of this application isincorporated by reference.

TECHNICAL FIELD

The present invention relates to a sensor apparatus and a predictionapparatus for use in predicting a brake cooling period following abraking event, and in particular relates to a sensor apparatus and aprediction apparatus for use in predicting a cooling period of anaircraft brake following a braking event.

BACKGROUND

Regulations require aircraft brakes to be able to handle an abortedtakeoff at any moment prior to the plane leaving the runway. Brakesshould not exceed a specified temperature, to avoid performancedegradation, so the regulations prohibit an aircraft from taking off ifits brakes are too hot (e.g. above 400° C.). To ensure that the brakesare cool enough even after use during taxiing out to the runway, it isrecommended that an aircraft is not dispatched if its brakes are above apredefined temperature (e.g. 150° C., as measured by a brake temperaturesensor), which is significantly lower than the maximum permittedtake-off temperature and allows for temperature increase during taxibraking.

Currently, the temperature of each brake pack on an aircraft ismonitored using thermocouples placed in the brake pack which providetemperature measurements to a brake temperature monitoring system (BTMS)comprised in the avionics systems of the aircraft. The BTMS providestemperature information based on the measured temperature of each brakepack on the aircraft to the flight crew, to enable them to determinewhether or not the brakes are cool enough to permit the aircraft to takeoff.

When all of the brake temperature sensors (i.e. the thermocouples) on anaircraft are functional, it is therefore not necessary to calculate abrake cooling time. However; for some aircraft a protocol (MMEL) existswhich covers situations in which one or more brake temperature sensorsare not functional (as well as other BTMS partial failure scenarios),and which may allow the aircraft to take off despite the non-functionaltemperature sensor(s) (or other partial failures).

For some cases the MMEL specifies that one when or more braketemperature sensors are non-functional, manual temperature measurementsshould be obtained for all brakes on the landing gear having thenon-functional sensor(s). Manual temperature measurements must be takenfrom outside the brake pack, and so do not represent the same quantityas the measurements obtained by the BTMS sensors in the brake packs, butthey can be used to qualitatively compare the temperature of differentbrakes on an aircraft.

If the manual temperature measurements for all of the brake packs havingnon-functional sensors are less than the manual temperature measurementsfor the hottest brake having a functional temperature sensor, then theMMEL permits a take-off determination to be made based only on thefunctional temperature sensors, and does not require a cooling time tobe calculated. In all other cases (and in cases where manual temperaturemeasurements are not obtained), the MMEL requires a brake cooling timeto be calculated and applied, according to rules provided in the MMEL.The MMEL cooling time calculation rules are conservative to ensure thatall brakes (including those with unknown temperatures, which may behotter than the other brakes) have cooled to below 150° C. beforeaircraft dispatch. As a result of the conservativeness built into theMMEL cooling time calculation rules, an aircraft with a non-functionalbrake temperature sensor may wait significantly longer before beingpermitted to take-off than would have been the case if all of its braketemperature sensors had been functional.

US 2006/0241819 describes a method to compute brake cooling times byobtaining brake temperature measurements at two points in time (asdetermined using a timer), calculating a rate of cooling based on themeasurements, and comparing the calculated rate to a stored temperatureprofile for brake cooling at an appropriate ambient temperature. A crudeestimate of cooling time is determined based on this comparison.However; the method of US 2006/0241819 requires a functional braketemperature sensor and therefore cannot be used as an alternative to theMMEL calculation rules in situations where one or more brake temperaturesensors of an aircraft are non-functional.

An improved system for predicting a brake cooling time is thereforedesired.

SUMMARY

A first aspect of the present invention provides an aircraft comprisinga torque sensor for measuring the torque reacted by a brake during abraking event; a wear sensor for measuring a wear state of the brake; anenvironmental sensor for measuring at least one ambient condition of theenvironment of the brake; and a brake cooling prediction apparatus forpredicting a brake cooling period following a braking event involvingthat brake, when measured values of the temperature of the brake are notavailable at least in respect of a time period including the brakingevent and the time of the predicting. The brake cooling predictionapparatus comprises a memory storing information relating to the thermalbehaviour of the brake, and a controller configured to receive a torquemeasurement from the torque sensor; receive a wear measurement from thewear sensor; receive an ambient condition measurement from theenvironmental sensor; and predict a cooling period required for thebrake to reach a predetermined temperature following the braking event,based on the received torque measurement, the received wear measurement,the received ambient condition measurement, and the information relatingto the thermal behaviour of the brake.

Optionally, the aircraft further comprises a temperature sensor formeasuring a temperature of the brake.

Optionally, the environmental sensor is for measuring one or more of:ambient temperature; air flow, wind direction, wind speed.

Optionally, the brake is an aircraft brake.

Optionally, the controller is configured to predict a cooling period bydetermining a maximum brake temperature as a result of the brakingevent, and by determining a cooling rate. The controller may beconfigured to determine the maximum brake temperature by determining anamount of energy input to the brake during the braking event, based onthe received torque measurement. The controller may be configured todetermine the maximum brake temperature by determining a thermal mass ofa component of the brake, based on the received wear measurement.Optionally, the controller is configured to determine the cooling ratebased on the determined maximum temperature, the received ambientcondition measurement, and the stored information relating to thethermal behaviour of the brake.

Optionally, when the aircraft further comprises a temperature sensor formeasuring a temperature of the brake, the controller is furtherconfigured to receive a temperature measurement from the temperaturesensor and to update the information relating to the thermal behaviourof the brake based on the received temperature measurement. Thecontroller may be configured to update the information by determining acorrection factor based on the received temperature measurement andapplying the determined correction factor to the information. Thecontroller may be configured to store the received temperaturemeasurement, and a time associated with the received temperaturemeasurement in the memory, to create or update a time-series of braketemperature measurements stored in the memory.

Optionally, the controller is further configured to receive anindication of a cooling fan state, and to predict the cooling periodbased additionally on the received indication of a cooling fan state.

Optionally, the information relating to the thermal behaviour of thebrake comprises one or more of: information relating to the past thermalbehaviour of the brake; a time-series of measurements of the temperatureof the brake; a mathematical model of the brake; a look-up table; amathematical relationship relating any two or more of: torque, wear,ambient condition; cooling fan state; information relating the thermalbehaviour of the brake to the thermal behaviour of a further brake.

Optionally, the controller is further configured to receive ameasurement of a temperature of a further brake, and to predict thecooling period based additionally on the received further braketemperature measurement. The memory may further store informationrelating the thermal behaviour of the brake to the thermal behaviour ofthe further brake. The controller may be further configured to predictthe cooling period based additionally on the information relating thethermal behaviour of the brake to the thermal behaviour of the furtherbrake. The further brake may be on the same axle as the brake.

Optionally, the information relating to the thermal behaviour of thebrake is based on the type of the brake.

Optionally, when the aircraft further comprises a temperature sensor formeasuring a temperature of the brake, the aircraft further comprises abrake temperature monitoring system, BTMS, wherein the predictionapparatus is configured to provide a predicted cooling period to theBTMS. The prediction apparatus may be configured to estimate a currentbrake temperature based on the received torque measurement, the receivedwear measurement, the received ambient condition measurement, and theinformation relating to the thermal behaviour of the brake. Theprediction apparatus may be configured to provide the estimated currentbrake temperature to the BTMS. A controller of the BTMS may beconfigured to select, as the basis for a determination of a currentbrake temperature and/or a predicted cooling period of a brake, one ormore of: a temperature measurement received from the brake temperaturesensor; a predicted cooling period received from the predictionapparatus; an estimated current brake temperature received from theprediction apparatus. The controller of the BTMS may be configured toperform the selection based on an operational state of the braketemperature sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic view of a brake cooling prediction systemaccording to an example;

FIG. 2a shows a schematic view of a sensor apparatus according to anexample;

FIG. 2b shows a schematic view of a prediction apparatus according to anexample;

FIG. 3 shows an example plot of measured brake temperature against timefor a first example aircraft brake;

FIG. 4 shows an example plot of measured brake temperature against timefor the first example aircraft brake and an example plot of measuredbrake temperature against time for a second example aircraft brake;

FIG. 5 shows an example plot of estimated brake temperature against timefor the first example aircraft brake and an example plot of measuredbrake temperature against time for the second example aircraft brake;and

FIG. 6 is a schematic view of an example aircraft comprising a brakecooling prediction system according to an example.

DETAILED DESCRIPTION

Aircraft, and in particular aircraft of airlines, are equipped with abrake temperature monitoring system (BTMS) for measuring and monitoringthe temperatures of the wheel brakes. A BTMS comprises a temperaturesensor for each wheel brake of each of the sets of wheels which may bebraked. Each of the temperature sensors is in communication with acentral computer, which is usually located in the avionics bay of theaircraft. Temperature values measured by each of the temperature sensorsmay thereby be communicated to the cockpit, for use by the flight crewin determining whether the brakes are cool enough for the aircraft topush back from the stand. As mentioned above, if one or more of the BTMStemperature sensors on an aircraft is non-functional, it may benecessary to calculate a cooling time (hereinafter referred to as a“cooling period”) after which all of the brakes of the aircraft will bebelow a preselected temperature (e.g. 150° C.).

The actual time required for a given brake to cool to a particulartemperature depends on various factors, including starting temperature,mass of the brake, specific heat capacity of the brake, and ambientconditions (e.g. ambient temperature, air flow, wind speed anddirection, etc.). The specific heat capacity of the brake depends on thetype of materials comprised in the brake and is expected to remainsubstantially constant over the operational life of a brake. Thestarting temperature will depend on the amount of energy that has beeninput to the brake (e.g. during a braking event) and on ambientconditions. The mass of the brake will depend on the amount and type ofmaterial comprised in the brake, and in particular will be affected bythe degree of wear of the brake discs. It is possible, in principle, todefine characteristic thermal behaviour of any given brake (e.g. basedon relationships between the above factors). The following disclosureseeks to provide a brake cooling period prediction system which combinesinformation relating to the thermal behaviour of a given aircraft brakewith current measurements of relevant factors, in order to generate afast and accurate cooling period prediction for that brake.

FIG. 1 shows an example brake cooling period prediction system 100. Thebrake cooling period prediction system 100 can be used to predict abrake cooling period following a braking event, and in particular abrake cooling period of an aircraft brake following landing and/ortaxiing of the aircraft. In the context of the current disclosure, theterm “braking event” is used to refer to any operation of the brakewhich causes energy to be input to the brake and therefore thetemperature of the brake to increase. A braking event may typicallycause the brake to heat up beyond an acceptable take-off temperature.The operation of the brake will typically be, e.g., for the purpose ofslowing an aircraft on which it is installed. A braking event willtypically occur during landing and/or taxiing of the aircraft. In thecurrent disclosure, the term “braking event” may be used to refer to asingle operation of the brake, or to multiple consecutive operations ofthe brake. However; for multiple operations of the brake to beconsidered as comprised in a single braking event, the intervening timeperiod between consecutive operations of the brake should be shortenough that the brake has not cooled to a desired temperature in thatintervening time period.

The brake cooling period prediction system 100 comprises a sensorapparatus 110, which is connected by a communications link 130 to aprediction apparatus 120. The communications link 130 may wired,wireless, or part wired and part wireless. The brake cooling periodprediction system 100 is configured such that the prediction apparatus120 is able to be located remotely from the sensor apparatus 10 when thebrake cooling period prediction system 100 is installed on an aircraft.For example, the sensor apparatus 110 may be located on or in a brakepack, whilst the prediction apparatus 120 is located on or in a fuselageof the aircraft (e.g. in an avionics bay of the aircraft). This meansthat the prediction apparatus 120 can advantageously be provided in anenvironment which is less harsh than the immediate environment of thebrake pack.

The brake cooling period prediction system 100 can be comprised in anaircraft avionics system, or can be connectable to an aircraft avionicssystem in any suitable manner, such that the brake cooling periodprediction system 100 is able to communicate measured temperature valuesto the aircraft avionics system. For example, the brake cooling periodprediction system 100 may be comprised in or connectable to a controllerof a BTMS of the aircraft. At least some components of the brake coolingperiod prediction system 100 can be configured to receive power via aconnection to an aircraft avionics system.

FIG. 2a shows the sensor apparatus 110 in more detail. The sensorapparatus 110 is for use in predicting a brake cooling period followinga braking event, e.g. a cooling period of an aircraft brake following anevent involving landing and/or taxiing of the aircraft. The sensorapparatus 110 comprises a torque sensor 210, for measuring the torquereacted by a brake during a braking event; a wear sensor 211, formeasuring a parameter relating to a wear state of the brake (e.g. brakedisc thickness, brake disc mass, or any other measurable parameter fromwhich a wear state of the brake can be determined); and an environmentalsensor 212, for measuring at least one ambient condition of theenvironment of the brake. In the context of this disclosure the“environment” of the brake is used to refer to the region surroundingthat brake and any elements comprised in that region and/or forcesacting in that region. The environment of a given brake should beconsidered to include all elements external to the brake which canpotentially affect the cooling period of that brake. It can include bothnatural elements (e.g. ambient temperature, wind, etc.) and artificialelements (e.g. other aircraft components, cooling fans or other items ofairport equipment, etc.). The sensor apparatus 110 may optionally alsocomprise a temperature sensor 213, for measuring a temperature of thebrake.

The torque sensor 210 is configured to transmit a measurement signalcontaining information about the torque reacted by a brake during abraking event to the prediction apparatus 120 via a communications link130 a. The wear sensor 211 is configured to transmit a measurementsignal containing information about a parameter relating to the wearstate of a brake to the prediction apparatus 120 via a communicationslink 130 b. The environmental sensor is configured to transmit ameasurement signal containing information about at least one ambientcondition of the environment of a brake to the prediction apparatus 120via a communications link 130 c. The temperature sensor 213 isconfigured to transmit a measurement signal containing information abouta temperature of a brake to the prediction apparatus 120 via acommunications link 130 d. Each of the communications links 130 a-d iscomprised in the communications link 130 of FIG. 1. Each of thecommunications links 130 a-d may be wired or wireless. One or more ofthe communications links 130 a-d may be combined into a single wired orwireless communications link for at least part of the transmission pathbetween the sensor apparatus 110 and the prediction apparatus 120.

The torque sensor 210 is configured to measure the torque reacted by abrake and transmit measured torque values to the prediction apparatus120. In some examples the torque sensor 210 is configured to transmit aseries of torque values during the course of a braking event. In otherexamples the torque sensor 210 is configured to measure a total torquereacted by a brake during a braking event and to transmit a total torquevalue for that braking event to the prediction apparatus 120. The torquesensor 210 can be of any suitable design. For example, on an aircrafthaving a classic bogie arrangement, the torque sensor 210 can comprise aTorque Pin of strain gauge type, located on a brake torque rod. On anaircraft without a bogie, it is proposed to use an optical load sensorto measure torque on an axle to which the brake is mounted.

The wear sensor 211 is configured to measure a wear state of a brake.For example, in a multi-disc aircraft brake pack, material is removedfrom the discs (due to frictional forces between the stators and rotors)during operation of the brake. Over the life time of a brake pack, asufficient amount of material will be removed from the discs to have anon-negligible effect on the mass of the brake. This is particularlytrue in the case of carbon brake discs. The wear sensor 211 isconfigured to measure a parameter relating to the wear of the brake insuch a way that the measurements of the parameter can be used todetermine a current mass of the brake. In some examples the wear sensor211 is configured to measure the thickness of one or more brake discscomprised in the brake, and to transmit a thickness value for the one ormore brake discs to the prediction apparatus 120. It will be appreciatedthat, provided that the geometry and material properties of the brakedisc are known, such a thickness value can enable the calculation of themass of the one or more brake discs. In some examples, the thickness ofall of the brake discs comprised in a brake pack is measured as a whole.

The wear sensor can be of any suitable design. For example, in the caseof a classic hydraulic aircraft brake, the wear sensor 211 can comprisea linear variable differential transformer (LVDT) sensor, or a HallEffect sensor, configured to measuring the linear displacement (wear) ofa component of the brake. Such a linear displacement sensor can belocated, for example, on the rear of the brake piston housing. In thecase of an electric brake comprising an e-brake controller, the brakewear is measured as part of the e-brake controller. This information canbe made available to the prediction apparatus 120. In such examples thewear sensor 211 comprises an e-brake controller of the brake (i.e. thebrake for which a cooling period is to be predicted).

The environmental sensor 212 is configured to measure an ambientcondition of the environment of the brake, and to transmit a value forthe measured ambient condition to the prediction apparatus 120. In someexamples the environmental sensor 212 is configured to measure aplurality of ambient conditions of the environment of the brake. Theambient condition can be any environmental condition which couldpotentially affect the cooling period of a brake. For example, theenvironmental sensor 212 can be configured to measure one or more of:ambient temperature; air flow, wind direction, wind speed. A higherambient temperature will increase the cooling period. An air flow (e.g.created by a cooling fan) will reduce the cooling period, by an amountdependent on the flow rate and volume. Similarly, a higher wind speedcan reduce the cooling period for brakes located such that they are inthe wind. Wind direction may affect whether or not a given brake is inthe wind, and therefore whether or not that brake will experience anadditional cooling effect as a result of the wind.

The environmental sensor 212 can comprise any sensor or combination ofsensors suitable for measuring the ambient condition(s). For example,the environmental sensor 212 can comprise a temperature sensor, anairflow sensor, a wind speed sensor, a wind direction sensor, or anycombination of such sensors. It is expected that, typically, theenvironmental sensor 212 will comprise plurality of sensors, which neednot be located near to each other or near to the brake. For example, acontroller of a brake cooling fan can measure an airflow generated bythat fan, ambient local temperature can be measured by the BTMS and/or afurther aircraft system. Wind data (wind speed, direction, ambient temp)can be measured by an aircraft system or can be provided by an airportsystem.

The temperature sensor 213, if present, is configured to measure atemperature of the brake and to transmit a measured temperature value tothe prediction apparatus 120. In some examples the temperature sensor213 is a temperature sensor associated with a BTMS of the aircraft.Indeed, in examples in which the system 100 is being used on an aircrafthaving a fully functional BTMS, it is expected that the temperaturesensor 213 will be present and will comprise a temperature sensorassociated with the BTMS. The temperature sensor 213 is located on or inthe brake pack, and is arranged to obtain a measurement of the internaltemperature of the brake pack. In some examples the temperature sensor213 comprises a thermocouple. The temperature sensor 213 can be arrangedto transmit a measured temperature value directly to the predictionapparatus 120. Alternatively, the temperature sensor 213 can be arrangedto transmit a measured temperature value to a BTMS controller, which inturn transmits the measured temperature value to the predictionapparatus 230.

FIG. 2b shows the prediction apparatus 120 in more detail. Theprediction apparatus 120 is for use in predicting a brake cooling periodfollowing a braking event, e.g. a cooling period of an aircraft brakefollowing an event involving landing and/or taxiing of the aircraft. Theprediction apparatus 120 comprises a memory 250 and a controller 260.The memory 250 stores information relating to the thermal behaviour ofthe brake (i.e. the brake for which a cooling period is to be predicted)(hereinafter referred to as “brake thermal information”). The memory 250can comprise any suitable implementation of a computer readable storagemedium, such as a hard drive, flash memory, non-volatile memory, etc.The controller 260 is configured to receive a torque measurement, a wearmeasurement and an ambient condition measurement from a sensor apparatus(e.g. the sensor apparatus 110). In some examples, the predictionapparatus 120 is configured to receive measurements from a plurality ofsensor apparatus, each of which is associated with a different brake ofan aircraft on which the prediction apparatus 120 is installed. Forexample, the prediction apparatus 120 may receive measurements inrespect of each individual brake comprised in an aircraft on which theprediction apparatus 120 is installed. In some examples the controller260 is further configured to receive a temperature measurement from asensor apparatus (e.g. the sensor apparatus 110). As mentioned above, inexamples in which the system 100 is being used on an aircraft having afully functional BTMS, the controller 260 may typically receive atemperature measurement from a temperature sensor comprised in orassociated with the BTMS.

The controller 260 is further configured to predict a cooling periodrequired for the brake to reach a predetermined temperature following abraking event, based on the received torque measurement, the receivedwear measurement, the received ambient condition measurement, and thebrake thermal information.

FIG. 2b shows the memory 250 and controller 260 comprised in a singleunit, which may, e.g., comprise a single housing containing thecontroller 260 and the memory 250. However; it is also possible for thememory 250 to comprise a separate unit from the controller, in whichcase the memory 250 will be connected to the controller 260 by acommunications link (which may be wired or wireless). For example, thecontroller 260 may be implemented as a remote storage device.

The brake thermal information can comprise one or more of: informationrelating to the past thermal behaviour of the brake; a time-series ofmeasurements of the temperature of the brake; a mathematical model ofthe brake; a look-up table; a mathematical relationship relating any twoor more of: torque, wear, ambient condition; cooling fan state; etc.FIG. 3 shows an example of brake thermal information in the form of aplot 310 of a time-series of measurements of the temperature of a brake.The temperature measurements cover a first time period 320 during whicha first braking event (represented by the peak 350) occurred (e.g.during landing and braking of the aircraft on which the brake isinstalled), a second time period 330 during which the brake was coolingfollowing the first braking event (including a minor peak representing asecond braking event during taxiing of the aircraft following landing),and a third time period 340 during which the brake was at ambienttemperature (so no further cooling occurred), until a third brakingevent (represented by the peak 360) occurred (e.g. during taxiing beforetake-off).

When all external influences remain constant, the brake will cool inaccordance with a characteristic cooling curve. The exact shape of thischaracteristic cooling curve will depend on the mass and specific heatcapacity of the brake, the starting temperature, and the ambientconditions. In some examples the brake thermal information can comprisea set of characteristic cooling curves, corresponding to differentcombinations of these variables.

The thermal behaviour of a given brake will be unique to that brake on afine scale. However; the thermal behaviour of brakes of the same type(i.e. brakes intended for use on the same landing gear of the same typeof aircraft, and from the same manufacturer) is expected to be verysimilar. The thermal behaviour of brakes of the same type may besufficiently similar that any differences can be considered negligiblefor the purposes of predicting a cooling period. The brake thermalinformation may therefore be based on the type of the brake. Forexample, an aircraft manufacturer may create predefined brake thermalinformation in respect of each different type of brake found on itsaircraft, and may store in the memory of a given prediction apparatusonly the predefined brake thermal information relating to the braketypes for which that prediction apparatus receives measurements.

In some examples the controller 260 is further configured to receive anindication of a cooling fan state, e.g. from the cooling fan, from adevice operated by ground crew, or from another aircraft system. Theindication may indicate whether the cooling fan has been activated, orthat it has been deactivated. For example, ground crew may communicateto the controller, directly from an electronic device used by the groundcrew or via another system of the aircraft, that a cooling fan has beenactivated and directed at the brake. It will be appreciated thatactivating a cooling fan directed at a brake will reduce the coolingperiod for that brake. Therefore, in such examples the controller 260 isfurther configured to predict the cooling period for the brake basedadditionally on the received indication of a cooling fan state. Thisfeature can be advantageous if a sensor apparatus is used whichcomprises an environmental sensor which is not capable of detecting thata cooling fan is blowing air at the brake.

In some examples the controller 260 is further configured to receive atemperature measurement from the sensor apparatus 110 (e.g. examples inwhich the sensor apparatus 110 comprises a temperature sensor 213). Insome such examples the controller 260 is configured to store thereceived temperature measurement in the memory 250, e.g. as part of thebrake thermal information. The controller 260 can be further configuredto update the brake thermal information based on the receivedtemperature measurement. For example, the controller 260 can beconfigured to store the received temperature measurement, and a timeassociated with the received temperature measurement in the memory 250,to create or update a time-series of brake temperature measurementsstored in the memory 250. As another example, if the brake thermalinformation comprises a set of characteristic cooling curves, the shapeof one or more of these curves can be updated to fit to the receivedtemperature measurement. In some examples, the controller is configuredto update the brake thermal information by determining a correctionfactor based on the received temperature measurement and applying thedetermined correction factor to the brake thermal information, e.g. inany suitable manner known in the art. Advantageously, continuouslyupdating the brake thermal information in this manner can ensure thatthe brake thermal information continuously adapts to reflect any changesin the thermal behaviour of the brake.

In some examples the controller 260 is further configured to receive ameasurement of the temperature of a further brake, e.g. from a sensorapparatus located on the further brake. For the sake of clarity and easeof distinction from the further brake, the brake (i.e. the brake forwhich a cooling period is to be predicted) will hereinafter be referredto as the “subject brake”. In some such examples the controller 260 isconfigured to store the further brake temperature measurement in thememory 250, such that the memory additionally (i.e. as well as storingbrake thermal information) stores information relating to the thermalbehaviour of a further brake (further brake thermal information). Insuch examples, the further brake information will comprise a time-seriesof temperature measurements. However; the further brake information mayalternatively or additionally comprise any of the information typesdescribed above in relation to the subject brake information.

The further brake can be any brake on the aircraft other than thesubject brake. However, advantageous examples are envisaged in which thefurther brake is on the same axle as the subject brake. Brakes on thesame axle are expected to experience very similar ambient conditions andloads, and therefore should exhibit similar cooling behaviour in anygiven situation, assuming similar environmental conditions. Insituations where brakes on the same axle might experience significantlydifferent environmental conditions (e.g. if one brake but not the otheris in sunlight, if one brake but not the other is in an airflow),temperature measurements from other common axle brake pairs experiencingsimilar differences in environmental conditions can be used to correctfor the effects of non-uniform environmental conditions. In a situationwhere current temperature measurements are available for a first brakeon a given axle but are not available for a second brake on that axle(e.g. because the second brake has a non-functional temperature sensor),the current temperature measurements for the first brake can be used asa basis for predicting a cooling period for the second brake.

FIG. 4 shows an example of further brake thermal information in the formof a plot 470 of a time-series of measurements of the temperature of afurther brake. FIG. 4a also includes the plot 320 of the time-series ofmeasurements of the temperature of the subject brake. The plot 470covers the same time period as the plot 320 and therefore includes thesame braking events. In this example, the further brake is on the sameaxle as the subject brake, and therefore its thermal behaviour duringthe illustrated time period is very similar to the thermal behaviour ofthe subject brake in that time period.

The differences in thermal behaviour between two brakes on the sameaircraft are expected to be substantially constant (at least over anexpected operating time period for which brake temperature measurementsare not available for the subject brake, e.g. because of a failed BTMStemperature sensor). A relationship between the subject brake and thefurther brake can therefore be determined. For example, when the furtherbrake is at a given temperature T_(x), the temperature of the subjectbrake can be assumed to be T_(x)+y, where y is a correlation factorrelating the temperature of the subject brake to the temperature of thefurther brake.

Using historical temperature-time data for the further brake and thesubject brake (or indeed any further brake and the subject brake), it istherefore possible to define a mathematical relationship relating thethermal behaviour of the subject brake to the thermal behaviour of thefurther brake, which can be used to, e.g., estimate a currenttemperature of the subject brake based on a current temperature of thefurther brake. The definition of such a mathematical relationship can bedone by the controller 260, based on stored further brake thermalinformation, e.g. during a process of predicting the cooling period forthe subject brake. Alternatively, a predefined mathematical relationshipcan be stored in the memory 250. Thus, in some examples in which thecontroller 260 additionally receives measurements of the temperature ofa further brake, the subject brake thermal information comprises amathematical relationship relating the thermal behaviour of the subjectbrake to the thermal behaviour of the further brake. Alternatively oradditionally, a mathematical relationship relating the thermal behaviourof the subject brake to the thermal behaviour of the further brake canbe comprised in further brake thermal information stored in the memory250.

It will be appreciated that the manner in which the controller predictsthe cooling period will depend on the nature of the brake thermalinformation. For example, if the brake thermal information comprises alook-up table, predicting the cooling period by the controller 260 maycomprise comparing one or more of the received measurements to entriesin the look-up table. As another example, if the brake thermalinformation comprises a mathematical relationship, predicting thecooling period by the controller 260 may comprise using one or more ofthe received measurements as inputs to the mathematical relationship.

In some examples the controller 260 is configured to predict a coolingperiod by determining a maximum brake temperature (i.e. the highesttemperature experienced by the brake as a result of the braking event)and a cooling rate. The maximum temperature can be determined, forexample, by determining an amount of energy input to the brake duringthe braking event. The amount of energy input to the brake during abraking event is proportional to the total amount of torque reacted bythe brake during that braking event. The controller 260 can thereforedetermine the energy input based on the received torque measurement. Thecontroller may be further configured to determine a maximum braketemperature by determining a mass of a component of the brake, based onthe received wear measurement. The mass of the brake component dependson the amount and type of material comprised in the brake component. Asdiscussed above, brake discs can experience a significant reduction inthe amount of material they comprise, over the lifetime of the brake,and thus a significant change in their mass. The manner in which brakediscs wear is well known, and the controller 260 can be programmed withappropriate information about a brake disc (e.g., geometry, materialtype, material properties) such that the controller 260 can determinethe mass of the brake disc based on a received wear measurement. Theinformation about the brake disc may be comprised in the brake thermalinformation.

If the total amount of energy input to the brake during a braking eventis known, the brake temperature before the braking event is known, thespecific heat capacity of the brake is known, and the mass of the brakeis known, then the maximum brake temperature can be determined based onthese values. In some situations (e.g. before a braking event duringlanding) it can be assumed that the brake temperature immediately beforethe braking event is equal to the ambient temperature in the brakeenvironment. This ambient temperature will generally be available fromthe environmental sensor 212 of the sensor apparatus 110. Thus, in someexamples the controller 260 is configured to determine a maximum braketemperature based on the received torque measurement, the received wearmeasurement and the received ambient condition measurement.

In other situations the brake temperature immediately before the brakingevent may be higher than ambient, for various reasons. Therefore, insome examples, the controller 260 is configured to determine a maximumbrake temperature based on the received torque measurement, the receivedwear measurement and the brake thermal information, wherein the brakethermal information comprises, e.g. an estimated or determined initialtemperature of the brake immediately prior to the braking event. Such anestimated or determined initial temperature can be, e.g., based on apredicted cooling period predicted in respect of a previous brakingevent, and/or based on a temperature of a further brake. Advantageously,the capability to determine a maximum brake temperature corresponding toa given braking event can enable an accurate cooling period for thebrake to be predicted even if no brake temperature measurements areavailable for that brake for the time period of the braking event (e.g.because a temperature sensor on that brake was non-functional at thetime of the braking event).

The controller 260 can be configured to determine a cooling rate basedon a determined maximum brake temperature, which may have beendetermined in any of the ways discussed above, and on the brake thermalinformation. The determined cooling rate may comprise a cooling curve. Acooling rate may be determined over the duration of a predicted coolingperiod. A determined cooling rate need not be constant over the timeperiod of the determined cooling rate.

As discussed above, the rate at which a brake will cool, assuming nofurther energy inputs, is a function of the maximum temperature,environmental conditions, the specific heat capacity of the brake andthe mass of the brake. The specific heat capacity of the brake dependson the type of material comprised in the brake and is expected to remainsubstantially unchanged over the life of the brake. It can therefore bepre-programmed into the controller 260. An accurate mass of the brakecan be determined by the controller 260 as described above, based on thereceived wear measurement. The environmental conditions can bedetermined by the controller 260 based on the received ambient conditionmeasurement(s). For example, the controller can be configured to selectand apply a correction factor (e.g. selected from a set of correctionfactors corresponding to various combinations of environmentalconditions, which are stored in the memory 250) corresponding to currentenvironmental conditions to the brake thermal information before usingthat brake thermal information as the basis of a cooling time periodprediction. Alternatively, in a particular example in which the brakethermal information comprises a set of cooling curves corresponding tovarious combinations of environmental conditions, the controller 260 maybe configured to select a cooling curve corresponding to the currentenvironmental conditions for use as the basis of a cooling time periodprediction.

In some examples the controller 260 is configured to determine a coolingrate for a subject brake based on a received measurement of thetemperature of a further brake. In such examples the determination ofthe cooling rate may be additionally based on information relating thethermal behaviour of the subject brake to the thermal behaviour of thefurther brake.

For example, consider a brake having a first (initial) temperature T₁. Abraking event then causes the brake temperature to rise to a maximumtemperature T₂, which can be calculated as described above using thetorque and wear measurements and the known brake characteristics of thesubject brake. Then, cooling occurs at a particular rate dependent onthe various factors described above. The cooling rate can be determinedbased on the determined maximum temperature T₂, the received ambientcondition measurement(s), and the subject brake thermal information,e.g. in the manner described above. However; assuming that currenttemperature measurements are available for the further brake (whichindicate the actual thermal behaviour of the further brake in theparticular situation), such further brake temperature measurements,together with the information which relates the subject brake thermalbehaviour to the further brake thermal behaviour, can be used to providean additional input to the cooling rate determination.

For example, it may be the case during a given cooling period that acurrent temperature of the subject brake, as determined based on afurther brake temperature measurement and the information relating thesubject brake thermal behaviour to the further brake thermal behaviour,is lower or higher than the current temperature given by the determinedcooling rate. In this situation the determined cooling rate can berecalculated based on the current subject brake temperature asdetermined based on a further brake temperature measurement and theinformation relating the subject brake thermal behaviour to the furtherbrake thermal behaviour.

FIG. 5 illustrates the use of further brake temperature measurements andinformation relating subject brake thermal behaviour to further brakethermal behaviour to predict a cooling period, in relation to thesubject brake and the further brake to which the time-series data ofFIG. 4 corresponds. FIG. 5 shows an example of further brake thermalinformation in the form of a plot 570 of a time-series of temperaturemeasurements of the temperature of a further brake. The plot 570 coversa time period which commences immediately after the time period coveredby the plot 470 of FIG. 4. The temperature measurements on which theplot 570 is based are received from a temperature sensor on the furtherbrake. FIG. 5 also includes a plot 520 of a time-series of measurementsof the temperature of the subject brake. The plot 570 covers the sametime period as the plot 520 and therefore commences immediately afterthe time period covered by the plot 420 of FIG. 4. During a first part581 of the time period of FIG. 5, the temperature measurements on whichthe plot 520 is based are received from a temperature sensor on thesubject brake. However; during a second part 582 of the time period ofFIG. 5, the temperature measurements on which the plot 520 is based areestimated by the controller 260 (e.g. because the temperature sensor onthe subject brake ceased to function at the end of the first part 581).The change from measured to estimated temperature values is indicated onFIG. 5 by the plot 520 changing from a solid line to a dotted line.

Some of the estimated temperature values on which the plot 520 is basedin the second part 582 of the time period are estimated by thecontroller based on the corresponding temperature measurements for thefurther brake, in addition to being based on the maximum temperature,the received ambient condition measurement(s) and the subject brakethermal information. In particular, the temperature values in the secondpart 582 up to and including T₁ (which is the temperature immediatelyprior to a braking event), and the temperature values in the second part582 after T₂ (which is the maximum temperature), are determined based ona cooling rate which has been determined based on a received measurementof the temperature of the further brake and on information relating thethermal behaviour of the subject brake to the thermal behaviour of thefurther brake, e.g. in the manner described above. By contrast, thedetermination of T₂ is performed as described above in relation to thedetermination of a maximum temperature, and is not based on the furtherbrake temperature measurements.

In some examples, e.g. examples in which the controller 260 isconfigured to store subject brake temperature measurements in the memory250, if the stored temperature cannot be updated because an aircraft onwhich the system 100 is installed is depowered, then once the aircraftis repowered a new start temperature for the subject brake can beaccurately determined, even if no current brake temperature measurementsare available for the subject brake, based on a measured temperature ofthe further brake and on information relating the thermal behaviour ofthe subject brake to the thermal behaviour of the further brake (e.g. amathematical relationship between the temperature of the further brakeat a given time and the temperature of the subject brake at that time).In most cases the aircraft will be re-powered after several hours andall brakes will be at ambient temperature. However; this may not alwaysbe the case. Accurately determining an initial temperature on power-upcan advantageously ensure that further temperature calculations based onthe received torque and wear measurements are as accurate as possible.

FIG. 6 shows an aircraft 600 on which a brake cooling period predictionsystem according to the examples (e.g. the brake cooling periodprediction system 100) is installed. The aircraft comprises a fuselage601, wings 602, and main and nose landing gear 604. Two wheels 603 areattached to each landing gear 604. Each wheel 603 has an associatedbrake pack (not visible) for braking that wheel. Each brake packcomprises a sensor apparatus, e.g. the sensor apparatus 110 describedabove. The aircraft 600 therefore comprises four separate sensorapparatus. The aircraft 600 further comprises a prediction apparatus,which is configured to communicate with each of the four sensorapparatus. The prediction apparatus may be a prediction apparatus 120 asdescribed above.

The aircraft 600 further comprises an avionics system 605, and in theparticular example the prediction apparatus is comprised in the avionicssystem 605. The avionics system 605 is located in an avionics bay orcompartment. In the particular example the avionics bay is in the noseof the aircraft below the cockpit, but it may be in a different locationdepending on the type of aircraft. The avionics system 605 comprises theelectronic systems associated with flying the aircraft, includingairborne communication and navigation systems and flight controlsystems. The avionics system 605 may comprise all of the electronicsassociated with communicating information to other parts of the aircraft600. The prediction apparatus may be configured to separately generateand process signals relating to each individual sensor apparatus fromwhich it receives measurements. However; alternative examples arepossible in which at least some of the data processing and/or predictingfor the different sensor apparatus is combined by the predictionapparatus.

Various alternative arrangements are possible for the predictionapparatus. For example, more than one prediction apparatus may beprovided, e.g. a prediction apparatus may be provided for eachindividual sensor apparatus comprised in the aircraft 600, or there maybe a prediction apparatus for each landing gear of the aircraft 600.There may be any number of prediction apparatus, up to and including thenumber of sensor apparatus. For example, an arrangement is envisaged inwhich a single prediction apparatus is provided in respect of eachlanding gear of the aircraft 600. In this example each predictionapparatus to receive four different sets of torque, wear and ambientcondition measurements, one set from each individual sensor apparatus onits landing gear. The prediction apparatus may be configured toseparately generate and process signals relating to each individualsensor apparatus on its landing gear. However; alternative examples arepossible in which at least some of the data processing and/or predictingfor the different sensor apparatus is combined by the predictionapparatus.

The aircraft 600 further comprises a BTMS (not shown), and in someexamples the brake cooling period prediction system is configured toprovide a predicted cooling period to the BTMS. In alternative examples,the brake cooling period prediction system is configured to estimate acurrent brake temperature based on the received torque measurement, thereceived wear measurement, the received ambient condition measurement,and the information relating to the thermal behaviour of the brake, andto provide the estimated current brake temperature to the BTMS. In suchexamples the BTMS can be configured to use the estimated current braketemperature received from the brake cooling period prediction system inplace of a brake temperature measurement from a brake temperaturesensor, e.g. in the event of failure of the brake temperature sensor.

For example, a controller of the BTMS can be configured to select, asthe basis for a determination of a current brake temperature and/or apredicted cooling period of a brake, one or more of: a temperaturemeasurement received from a brake temperature sensor; a predictedcooling period received from the brake cooling period prediction system;and an estimated current brake temperature received from the brakecooling period prediction system. The controller of the BTMS can beconfigured to perform the selection based on an operational state of thebrake temperature sensor.

The above embodiments are to be understood as illustrative examples ofthe invention. It is to be understood that any feature described inrelation to any one embodiment may be used alone, or in combination withother features described, and may also be used in combination with oneor more features of any other of the embodiments, or any combination ofany other of the embodiments. Furthermore, equivalents and modificationsnot described above may also be employed without departing from thescope of the invention, which is defined in the accompanying claims.

The invention claimed is:
 1. An aircraft comprising: a torque sensorconfigured to measure torque reacted by a brake during a braking event;a wear sensor configured to measure a wear state of the brake; anenvironmental sensor configured to measure at least one ambientcondition of an environment of the brake; and a brake cooling predictionapparatus configured to predict a brake cooling period following abraking event involving the brake, when measured values of a temperatureof the brake are not available at least in respect of a time periodincluding the braking event and a time of predicting the brake coolingperiod, the brake cooling prediction apparatus comprising: anon-transitory memory storing information relating to a thermal behaviorof the brake; and a controller configured to: receive a torquemeasurement from the torque sensor; receive a wear measurement from thewear sensor; receive an ambient condition measurement from theenvironmental sensor; and predict a cooling period required for thebrake to reach a predetermined temperature following the braking event,based on the received torque measurement, the received wear measurement,the received ambient condition measurement, and the stored informationrelating to the thermal behavior of the brake.
 2. The aircraft accordingto claim 1, further comprising a temperature sensor configured tomeasure a temperature of the brake.
 3. The aircraft according to claim2, wherein the controller is further configured to receive a temperaturemeasurement from the temperature sensor and to update the informationrelating to the thermal behavior of the brake based on the receivedtemperature measurement.
 4. The aircraft according to claim 3, whereinthe controller is configured to store the received temperaturemeasurement, and a time associated with the received temperaturemeasurement in the non-transitory memory, to create or update atime-series of brake temperature measurements stored in thenon-transitory memory.
 5. The aircraft according to claim 2, furthercomprising a brake temperature monitoring system (BTMS) wherein thebrake cooling prediction apparatus is configured to provide thepredicted cooling period to the BTMS.
 6. The aircraft according to claim5, wherein the brake cooling prediction apparatus is configured toestimate a current brake temperature based on the received torquemeasurement, the received wear measurement, the received ambientcondition measurement, and the information relating to the thermalbehavior of the brake, and to provide the estimated current braketemperature to the BTMS.
 7. The aircraft according to claim 6, wherein acontroller of the BTMS is configured to select, as the basis for adetermination of at least one of a current brake temperature and apredicted cooling period of a brake, one or more of: the temperaturemeasurement received from the brake temperature sensor; the predictedcooling period received from the prediction apparatus; the estimatedcurrent brake temperature received from the brake cooling predictionapparatus.
 8. The aircraft according to claim 7, wherein the controllerof the BTMS is configured to select one or more of the temperaturemeasurements, the predicted cooling period and the estimated currentbrake temperature based on an operational state of the brake temperaturesensor.
 9. The aircraft according to claim 1, wherein the environmentalsensor is configured to measure one or more of: ambient temperature; airflow, wind direction, and wind speed.
 10. The aircraft according toclaim 1, wherein the controller is configured to predict the coolingperiod by determining a maximum brake temperature as a result of thebraking event, and by determining a cooling rate.
 11. The aircraftaccording to claim 10, wherein the controller is configured to determinethe maximum brake temperature by: determining an amount of energy inputto the brake during the braking event, based on the received torquemeasurement; and determining a thermal mass of a component of the brake,based on the received wear measurement.
 12. The aircraft according toclaim 10, wherein the controller is configured to determine the coolingrate based on the determined maximum brake temperature, the receivedambient condition measurement, and the stored information relating tothe thermal behavior of the brake.
 13. The aircraft according to claim1, wherein the controller is further configured to receive an indicationof a cooling fan state, and to predict the cooling period basedadditionally on the received indication of a cooling fan state.
 14. Theaircraft according to claim 1, wherein the information relating to thethermal behavior of the brake comprises one or more of: informationrelating to a past thermal behavior of the brake; a time-series ofmeasurements of the temperature of the brake; a mathematical model ofthe brake; a look-up table; a mathematical relationship relating any twoor more of: torque, wear, ambient condition; cooling fan state; andinformation relating the thermal behavior of the brake to the thermalbehavior of a further brake.
 15. The aircraft according to claim 1,wherein the controller is further configured to receive a measurement ofa temperature of a further brake, and to predict the cooling periodbased additionally on the received further brake temperaturemeasurement.
 16. The aircraft according to claim 15, wherein thenon-transitory memory further stores information relating the thermalbehavior of the brake to the thermal behavior of the further brake, andwherein the controller is further configured to predict the coolingperiod based additionally on the information relating the thermalbehavior of the brake to the thermal behavior of the further brake. 17.The aircraft according to claim 15, wherein the further brake is on anaxle for the brake.
 18. The aircraft of claim 1, wherein the controlleris further configured to prohibit a take-off of the aircraft until afterexpiration of the predicted cooling period.
 19. An aircraft brakecooling prediction apparatus configured to predict a brake coolingperiod and comprising: a non-transitory memory storing informationrelating to thermal behavior of the brake, and a controller configuredto: calculate a predicted cooling period required for the brake to reacha certain temperature condition following a braking event, wherein thecalculation uses: a torque measurement received from a torque sensorsensing a torque reacted by the brake; a wear measurement received froma wear sensor sensing a wear state of the brake; an ambient conditionmeasurement received from an environmental sensor, and the storedinformation relating to the thermal behavior.
 20. The aircraft brakecooling prediction apparatus of claim 19, wherein the controller isfurther configured to prohibit a take-off of the aircraft until afterexpiration of the predicted cooling period.
 21. The aircraft brakecooling prediction apparatus of claim 19, wherein the controller isfurther configured to prohibit a take-off of the aircraft until afterthe brake has cooled to the specific temperature.
 22. A method topredict a brake cooling period comprising: measuring a torque reacted bya brake during a braking event of an aircraft brake; measuring wear by awear sensor monitoring a wear state of the brake; measuring at least oneambient condition of the environment of the brake; and calculating by acontroller a predicted cooling period required for the brake to cool toa specific temperature condition following a braking event, wherein thecalculation is based on the measured torque measurement, the measuredwear, the measured at least one ambient condition and informationrelating to thermal behavior of the brake retrieved form anon-transitory memory accessible by the controller.
 23. The method ofclaim 22, further comprising prohibiting a take-off of the aircraftuntil after the predicted cooling period.
 24. The method of claim 22,further comprising prohibiting a take-off of the aircraft until afterthe brake has cooled to the specific temperature.
 25. The method ofclaim 22, wherein the controller is further configured to prohibit atake-off of the aircraft until after the brake has cooled to thespecific temperature.